The use of benzotriazole and tolutriazole as corrosion inhibitors for copper and its alloys is well known. It has been used to prevent the corrosion of copper parts during manufacture and storage.
Benzotriazole has also been used to extend the useful life of polyurethane and thermoplastic acrylic lacquers when applied to a copper substrate. These lacquers when applied to a copper substrate. These lacquers provide good protection for 3-5 years of outdoor exposure. Yellowing and other signs of degradation are noted only after a prolonged period. I. R. A. Christie et al, Trans. Inst. Metal Finishes, 50, 19(1972).
Lacquers based on thermoplastic acrylic resins and polyurethane lacquers are not affected adversely when prepared using manufacturing equipment that contains copper or its alloys. They do not become contaminated with copper or its alloys. They do not become contaminated with copper during application when exposed to pipes, spray nozzles, etc. that are fabricated from metals containing copper. 2-Hydroxyphenylbenzotriazole ultraviolet stabilizers do not develop color when used in these lacquers. As Christie points out, such lacquers will be degraded more rapidly if they are applied over a copper or brass substrate. Environmental weathering of the metal will cause corrosion. The copper compounds produced by corrosion are soluble in the lacquer and will increase the rate of degradation upon weathering and stain the coating.
In contrast to the behavior of thermoplastic acrylic lacquers and polyurethane lacquers, thermosetting acrylic enamels and other paints that are cured using acid catalysts will aggressively attack copper and copper containing alloys such as brass and become contaminated with ionic copper. Such contamination can occur during paint manufacture and during application by contacting copper containing pipes, mixing equipment, spray nozzles, etc. Such contaminated enamels are discolored from the start and suffer from a decrease in stability upon exposure to light. These paints tend to lose gloss and crack sooner than such paints that have not been exposed to sources of copper. The addition of 2-hydroxyphenylbenzotriazoles or 2-hydroxybenzophenones to copper contaminated paints will result in immediate discoloration. It has been found that the use of benzotriazole or tolutriazole will decrease the extent of such copper contamination and improve both the color and durability of acid cured thermoset enamels.
Acid curable thermoset enamels are rapidly displacing thermoplastic lacquers. One of the major reasons for this change is technology stems from environmental considerations. Thermoplastic acrylic lacquers require a greater use of organic solvents to obtain a sprayable viscosity than acid curable enamels. On drying the solvents emitted from thermoplastic paints contribute more to air pollution. Additionally, thermoset automobile enamels have greater solvent resistance and thus resist degradation by inadvertent contact with gasoline and motor oil.